Even though functional neuroimaging techniques have been available for decades, they have generated only limited evidence of developmental plasticity. In human studies, brain -organizational changes during development have been mostly inferred from structural imaging and behavioral data. Our previous positron emission tomography studies in brain-damaged children and adults suggested pronounced functional reorganization following congenital and early postnatal lesion. We propose to approach the issue of developmental plasticity by means of functional magnetic resonance imaging (fMRI). The proposed research will examine (i) developmental changes of normal brain organization and (ii) functional reorganization following brain damage (early versus late). It will be performed in close cooperation with investigators of two existing NIH-funded centers for the study of cognitive and language development and the effects of focal brain damage. We will study 96 healthy subjects, evenly distributed across 4 age groups (6-8, 9-12, 13-17, and 18-50 years), using fMRI with two language paradigms (picture naming, syntactic decoding) and one motor task (finger movement). Studies of healthy subjects will provide reference data for the additional study of 20 pediatric and 20 adult patients with left hemisphere damage. Activation measures will be taken for multiple regions of interest, which will be traced on high-resolution anatomical MRIs of each individual brain. Our hypotheses are based on evidence of an experientially influenced interplay of constructive and regressive events in normal brain development. We expect that regressive events (e.g., synaptic pruning) may be partially suspended in reorganization after brain lesion. We specifically hypothesize that (a) task-related activations become more focal and lateralized during normal development, (b) left hemisphere lesion results in interhemispheric reorganization of language and motor processing, (c) reorganization is more pronounced after early (compared to late) lesion, and (d) regional patterns of reorganization differ between functional domains (language versus motor). Findings are expected to contribute to the understanding of compensatory plasticity in development.